In the manufacture of semiconductor devices, it is often necessary to connect multiple components of the semiconductor device together with an electrically conductive connector so that an electrical connection can be formed therebetween in use.
The conductive connector may be formed using ball grid array (BGA) technology, which involves depositing solder balls onto a substrate of an electronic component. The solder balls are subjected to soldering to thereby form conductive connectors to conduct electricity.
Prior to the deposition of solder balls onto the substrate, it is necessary to also deposit a flux material on the substrate so that the solder balls can adequately adhere to the substrate.
Current BGA technology uses a pin block to dispense solder flux onto the substrate. A known pin block and method of use is disclosed in U.S. Pat. No. 5,816,481. A disadvantage with the method disclosed in U.S. Pat. No. 5,816,481 is that an insufficient quantity of flux material is often deposited by the pins at the soldering site of the substrate. An insufficient quantity of flux material leads to inadequate soldering. This may cause the semiconductor device to fail in use.
The pins disclosed in U.S. Pat. No. 5,816,481 also have the disadvantage of depositing an excess of flux material onto the substrate. An excess of flux results in flux residue accumulating on the substrate after soldering. Excess flux residue may result in post-soldering cleaning problems.
Another problem associated with excess flux is that solder balls may merge with neighbouring solder balls. This results in an uneven ball size distribution on the substrate causing coplanarity problems at the conductive solder ball connectors, which may result in failure of the semiconductor device.
Accordingly, it is important for a precise amount of flux material to be deposited on the substrate at soldering sites.
Referring to FIGS. 1A to 1D, there is shown a schematic diagram of a known flux imprinting process. In the known flux imprinting process, the flux material is imprinted on the substrate using a flux imprinting device. This device comprises an array of flux pins 10 which are mounted within a chamber 12. An enlarged view of one of the flux pins 10 in FIGS. 1A to 1D is shown in FIG. 1. Referring to step 1 of FIG. 1A, the array of flux pins 10 are mounted within a moveable chamber 12 comprising a housing 14, in which reside proximal ends 16 of the pins 10. Each of the pins 10 is biased by springs 18 in a direction shown by arrow 20 toward the distal ends 22 of the pins 10. The distal ends 22 of the pins 10 are immersed in the flux material 24 in tray 26 to coat the distal ends 22 with the flux material 24.
In step 2 of FIG. 1B, the pins 10 are removed from the flux material 24 and the distal ends 22 of the pins 10 are coated with the flux material 24.
In step 3 of FIG. 1C, the pins 10 are lowered onto a substrate 28 in a direction shown by arrow 32 to deposit the flux material 24 thereon. The substrate 28 includes a plurality of recesses 30 on which the flux material 24 is to be deposited.
In step 4 of FIG. 1D, the pins 10 are released from the substrate 28 in a direction shown by arrow 34.
Referring now in particular to FIG. 1B, it can be seen that a flux bridge 24a is formed between the pins 10a and 10b due to flux creep over prolonged use of the flux imprinting device.
The contributing factors for flux creeping or crawling on the pin 10 is due to the surface energy of the cylindrical surface 23 being constant along the longitudinal axis 21. This constant surface energy causes flux to spread out along the cylindrical surface 23 to achieve equilibrium. The surface energy of the taper surface 25 increases with its circumference along the longitudinal axis 21 and encourages flux to move towards the larger circumference.
The accumulation of flux on the pins, after successive dipping in flux material, results in the flux material 24 tending to creep up the shafts of the pins 10 in a direction toward the proximal ends of the pins 10. This is known as “flux creep” or “flux crawl”.
The formation of flux bridges 24a results in an uneven deposition of the flux material 24a on the substrate 28 as shown by arrow 38 in FIG. 1D.
A further problem with flux creep is that it causes a reduced amount of flux that is adhered on the distal end 22 because the bulk of the flux is ‘pulled’ up the pin shaft. The reduced amount of flux deposited on the distal end 22 results in a reduced amount of flux being deposited on the substrate. This causes an unequal amount of flux deposition on the substrate which may result in defective soldering. This phenomena is particularly pronounced when a flux having a low viscosity is used.
Accordingly, it would be an advantage if embodiments of the invention provided pins which could overcome or at least ameliorate one or more of the disadvantages described above.